Animal cell culture in stirred bioreactors: observations on scale-up

The scale-up of stirred tank bioreactors from 0·02 m³ to a 0·3 m³ commercial plant is discussed for hybridoma suspension cultures. Schemes for dissolved oxygen control with sparged air in serum containing media are described, as well as mechanical breakage of foam in small and large bioreactors. Porous metal spargers (180–200 × 10⁻⁶ m) were found to produce foams which were hard to control. Aeration with larger (≥ 0·001 m) multihole spargers is recommended.

Combined cell damage due to foam formation and control, and possible damage at mechanical seals or submerged bearings, were found to have no measurable effect on cell growth relative to roller bottle production. Hybridomas are shown to withstand significant impeller tip speed ( > 1 m s⁻¹) and fluid turbulence as evidenced by impeller Reynolds numbers in excess of 10⁵. The size of the energy-dissipating terminal eddies was calculated to be greater than ten-fold that of the hybridoma cells. The specific fluid turnover rate was employed as the scale-up criterion.     

Animal cell culture in stirred bioreactors: Observations on scale-up

Scale-up of stirred tank bioreactors from 0.02 m³ to 0.3 m³ commercial plant is discussed for hybridoma suspension culture. Schemes for dissolved oxygen control with sparged air in serum containing media are described as well as mechanical breakage of foam in small and large bioreactors. Porous metal spargers (180?200×10^?6 m) are found to produce foams which are hard to control. Aeration with larger (> 0.001 m) multihole spargers is recommended. Combined cell damage due to foam formation and control, and possible damage at mechanical seals or submerged bearings, are found to have no measurable effect on cell growth relative to roller bottle production. Hybridomas are shown to withstand significant impeller tip speed (> 1 ms^?1) and fluid turbulence as evidenced by impeller Reynolds numbers in excess of 10⁵. The size of the energy dissipating terminal eddies is calculated to be > 10-fold that of the hybridoma cells. Specific fluid turnover rate is employed as the scale-up criterion.     

Spermatogonial stem cell transplantation, cryopreservation and culture.

Testis cells of a fertile male mouse can be transplanted to the seminiferous tubules of an infertile male, where the donor spermatogonial stem cells will establish spermatogenesis and produce spermatozoa that transmit the donor haplotype to progeny. In addition, stem cells can be cryopreserved for long periods, thereby making male germ lines immortal. Recently, mouse testis cells have been cultured for longer than 3 months and, following transplantation, produced spermatogenesis. These techniques are likely to be applicable to many species, since rat testis cells can be cryopreserved and generate spermatogenesis in the seminiferous tubules of immunodeficient mice.     

From 3D cell culture to organs-on-chips

3D cell-culture models have recently garnered great attention because they often promote levels of cell differentiation and tissue organization not possible in conventional 2D culture systems. We review new advances in 3D culture that leverage microfabrication technologies from the microchip industry and microfluidics approaches to create cell-culture microenvironments that both support tissue differentiation and recapitulate the tissue-tissue interfaces, spatiotemporal chemical gradients, and mechanical microenvironments of living organs. These 'organs-on-chips' permit the study of human physiology in an organ-specific context, enable development of novel in vitro disease models, and could potentially serve as replacements for animals used in drug development and toxin testing.     

Mammalian cell culture processes.

Over the past year, mammalian cell culture research has been aimed at investigating the influence of culture conditions on viability, productivity and the consistency of post-translational modifications. Studies of the effect of medium conditions and the development of kinetic models are being made in relation to current efforts to develop fed-batch strategies that will optimize recombinant protein production processes. Recent advances have included novel biosensor and bioreactor developments. New technologies have also been applied to investigate high cell density bioreactor and culture conditions.     

Large-scale insect cell culture.

Significant advances have been made over the past year in our understanding of the protective mechanisms, both fluid-mechanical and biological, of media additives on suspended animal cells. The degree of protection offered by different additives, such as pluronic polyol, appears to be cell-type dependent, varying quite dramatically not only between insect and mammalian cells, but also between different insect cell lines themselves.     

Animal cells in culture are microorganisms

Pick up any textbook with ‘Microbiology’ in the title and observe the scant to nonexistent treatment of animal cells in culture. Viruses do not suffer from such an exclusion. Chapters abound regaling the molecular niceties of the complex dances their components undergo while infecting bacteria or animal cells in culture. Indeed, it is normally in the latter sense only that any recognition is given to the existence of animal cells in culture. Such views pervade even the minds of those who initiate and direct activities of societies whoseraison d’être is the growth and exploitation of animal cells in culture. The author of this editorial was appointed to a Chair in Microbiology at the University of Surrey in 1983 and has worked on the growth and use of animal cells in culture continuously since 1970; he, therefore, had to reconcile his position in the university with his chosen calling. In this he was helped by undergraduates too numerous to mention who struggled mightily with essays which asked the question; are animal cells in culture microorganisms? What follows is a digest of their efforts and the views of the author.